The present invention relates to a pulp sheet or a pulp molding to be used as a packing material (inclusive of a wrapping material) for a container, a tray, or the like; and to a method for producing such a pulp sheet and a pulp molding.
Heretofore, a foamed material of a synthetic resin such as polystyrene, polyethylene has been much used as a packing material from the point of view of its characteristic such as strength, shock absorbency, proccessability. It is however difficult to incinerate waste of the foamed material from the point of view of the pollution of the environment. Therefore, the foamed material is usually buried as waste in a natural environment. The foamed material however remains for a long term because it has no biodegradability. Hence, there is a problem that the foamed material may spoil a fine sight or pollute the environment.
On the other hand, a pulp sheet, its press molding or a pulp molding, which mainly consists of pulp obtained from waste paper such as newspaper, magazine paper or corrugated board through careful selection for removing foreign substance after maceration with water, can be reused as a pulp raw material if it is macerated with water. Moreover, since it has natural degradability, there is no problem caused by remaining characteristic as in a synthetic resin. For this reason, such a pulp sheet molding or pulp molding has been widely used as a packing material recently.
The packing material composed of the background-art pulp sheet molding or pulp molding was, however, harder less flexible and less shock absorbent than that of the synthetic resin such as polystyrene or polyethylene. Therefore, there was a problem that the article packed in the packing material might be scratched by the packing material during packing, transportation or unpacking.
The present invention is designed to solve these problems and an object of the present invention is to provide a pulp packing material (inclusive of a pulp sheet and its press molding, and a pulp molding) having little influence on the environment, sufficient hardness to retain its shape, and sufficient flexibility and shock absorbency to avoid injury of an article packed in the packing material.
Another object of the present invention is to provide a pulp packing material having little influence on the environment, sufficient hardness to retain its shape, and sufficient smoothness to avoid injury of an article packed in the packing material.
According to an aspect of the present invention, the pulp packing material comprises a first layer containing crosslinked pulp as a main component, and a second layer made of a non-crosslinked material. Hence, the pulp packing material can be given flexibility and shock absorbency by the crosslinked first layer, and shape retentivity by the non-crosslinked second layer.
In the above pulp packing material, preferably, the second layer may contain pulp or biodegradable plastics as a main component. Hence, the pulp packing material thus obtained is excellent in terms of protection of the environment because it can be degraded by microorganisms or the like even in the case where it is disposed as waste.
Further, in the above pulp packing material, preferably, at least one surface of the pulp packing material may be covered with a film of plastics. Hence, the surface with the film of plastics is smoothened so that the packed article can be hardly injured.
Further, according to another aspect of the present invention, the pulp packing material comprises a sheet containing non-crosslinked pulp as a main component, and a film of plastics that covers at least one surface of the sheet. Hence, shape retentivity is ensured by the non-crosslinked pulp layer. Moreover, the surface with a film of plastics is smoothened so that the packed article can be hardly injured.
According to a further aspect of the present invention, there is provided a method for producing a pulp packing material which comprises the steps of: performing sheet making for producing a first layer containing crosslinked pulp as a main component and a second layer containing non-crosslinked pulp as a main component; and sticking the first and second layers to each other. According to the method, sheets of the first and second layers can be produced respectively by use of a background-art pulp-sheet making apparatus, and then these sheets can be stuck and laminated onto each other. Thus, a packing sheet satisfying the foregoing objects can be provided.
In another method, preferably, a first layer containing crosslinked pulp as a main component and a second layer containing non-crosslinked pulp as a main component are produced in first and second molds, respectively. The first and second layers are cramped between the first and second molds and then, stuck to each other. According to this method, the process from the step of forming the pulp moldings of the respective layers to the step of sticking and laminating the moldings onto each other can be performed continuously by use of the first mold and the second mold having a shape opposed to the shape of the first mold. Hence, a packing molding article satisfying the foregoing objects can be obtained with the advantage of reduction in production time and cost.
According to a further aspect of the present invention, a first layer containing crosslinked pulp as a main component and a second layer containing non-crosslinked pulp as a main component are produced by means of sheet-making respectively, and then the first and second layers are stuck onto each other and press-molded. According to this aspect, sheets of the first and second layers can be produced respectively by use of a conventional pulp-sheet making apparatus. A packing molding article having a predetermined shape and satisfying the foregoing objects can be also obtained from these sheets.
According to a further aspect of the present invention, after at least one surface of a sheet containing non-crosslinked pulp as a main component is covered with a film of plastics, the sheet with the film of plastics is heated. According to this aspect, the surface of the pulp sheet or pulp molding article having shape retentivity can be smoothened.